The present invention relates to cardiac defibrillators. More particularly, this invention is directed toward a blocking circuit that prevents an undesirable leakage current from being applied to a patient's heart when the patient is connected to a cardiac defibrillator for an extended period of time.
Cardiac defibrillators are devices that deliver high-voltage pulses to a patient's heart for the purpose of terminating an episode of cardiac fibrillation. Some defibrillators are used by physicians in emergencies - i.e., when a patient unexpectedly suffers an episode of cardiac fibrillation. Other types of defibrillator systems are used in different contexts. For example, some defibrillators are implanted within a patient, and continually monitor the patient's heart to determine whether the heart is fibrillating. If the heart begins to fibrillate, the implanted defibrillator will apply a defibrillation pulse to the heart to terminate the episode of fibrillation.
Defibrillators are used in yet another context when a physician wishes to adjust the voltage level at which an implanted defibrillator has been set to apply defibrillation pulses. The appropriate voltage level may vary considerably from patient to patient. For example, the voltage to be applied may depend on the condition of the defibrillator's leads, which are used to apply defibrillation pulses to the heart, as well as the characteristics of each individual's heart. As a result, before the appropriate defibrillation voltage level is selected for an implantable defibrillator, the physician will typically induce fibrillation in the patient's heart to determine what voltage level is required to terminate fibrillation for that patient. After attempting to terminate the fibrillation with pulses having low voltage levels, the physician will typically raise the level of the applied voltage until a level that is effective for terminating the episode is reached. Defibrillation systems used for this method of determining defibrillation thresholds are commonly known as defibrillator system analyzers.
Although defibrillator system analyzers may be used by physicians to determine a patient's defibrillation threshold, these analyzers must often be connected to the patient for extended periods of time to allow the physician to complete the threshold analysis. In order to reduce the likelihood of applying a leakage current to the patient, it would be desirable to provide a leakage current blocking circuit. An effective leakage current blocking circuit would help prevent leakage-current induced corrosion of the leads of those cardiac defibrillators that are implanted in a patient. The blocking circuit should be manufacturable in an efficient and cost-effective manner.